Field of the Invention
Preferred example relates to the art of a power transmission unit for hybrid vehicles having selectable one-way clutch adapted to selectively limit a torque transmission only in one direction.
Discussion of the Related Art
A hybrid vehicle is powered not only by an engine but also by a motor or motor-generator (as will be called the “motor” hereinafter). In order to distribute powers of those prime movers while changing a speed, the hybrid vehicle is provided with a planetary gear unit. One example of the hybrid vehicle of this kind is described in JP-A-2013-086654. The motor produces heat in both situations to be energized to generate a mechanical power and to be rotated passively to generate an electric power. Heat is also generated in the planetary gear unit as a result of torque transmission by a friction between gears. In order to cool and lubricate the motor and the planetary gear unit, in the hybrid vehicle taught by JP-A-2013-086654, lubrication oil is delivered to the motor and the planetary gear unit from an oil pump.
The lubrication oil is delivered to the motor and the planetary gear unit through oil passages formed in a housing and a rotary shaft, and hence an amount of oil delivered to the motor and the planetary gear unit is governed by a cross-sectional area of the oil passage. That is, a feeding amount of the oil to a lubrication site has to be fixed depending on the cross-sectional area of the oil passage in spite of a change in a torque transmitting condition of the planetary gear unit during activation of the motor. For this reason, a discharging amount of the oil pump has to be adjusted to the largest required amount of the oil for lubricating and cooling the lubrication site. That is, the oil is delivered excessively to the planetary gear unit even when the planetary gear unit is not transmitting torque and this may cause a power loss.